In large and heavily loaded bearings, the forces of friction between the moving parts are also large. Bearings of this kind are used, for example, in the press rolls of a paper machine. In particular, the friction due to the thermal expansion of the shaft is a problem in bearings that permit free axial movement. This problem does not arise in hydrostatic bearings, because a layer of lubricating oil is often also arranged between the outer sleeve and the bearing block. In this case, the entire bearing can move axially within the bearing block and adjust to variations in the length and angle of the shaft. Special pockets are used to distribute the lubricant.
Thermal expansion can be eased in the aforementioned hydrostatic bearings, but there are no simple means to lighten other types of bearings. If the inner sleeve of the bearing can rotate, the outer sleeve of the bearing is fitted to the bearing block with a sliding fit and the inner sleeve with a tight fit. In this case, it is intended that the thermal expansion of the bearing will be accommodated through the relative movement of the outer sleeve and the bearing block. Correspondingly, if the outer sleeve can rotate, it is intended that the thermal expansion will be accommodated through the relative movement of the shaft collar and the inner sleeve of the bearing. However, large friction forces may prevent this movement, when great stresses will be imposed on the bearing members. The bearing will be loaded, even if no axial force acts on the shaft. The additional stress reduces the operating life of the bearing and may even lead to structural failure.